Preparation, characterization, and investigation of the catalytic property of α-Fe2O3-ZnO nanoparticles in the photodegradation and mineralization of methylene blue

The alpha-Fe2O3 and ZnO nanoparticles (NPs) were synthesized and mixed to obtain the alpha-Fe2O3-ZnO nanocomposite (NC). Some identification techniques of XRD, FTIR, DRS, and SEM-EDX were used to characterize the individual and composite samples. XRD results showed the crystallite sizes of 26, 32, and 30 nm (by the Scherrer equation) and 42, 65, and 34 nm (by the Williamson-Hall equation) for the as-prepared ZnO, alpha-Fe2O3 and alpha-Fe2O3-ZnO catalysts, respectively. In the DRS study, the absorption edge wavelengths of 478, 392, and 554 nm correspond to the band gap energies of 2.59, 3.16, and 2.73 were estimated for the alpha-Fe2O3, ZnO and alpha-Fe2O3-ZnO samples, respectively. Enhanced activity of the NC sample in the photodegradation of methylene blue (MB) was observed which was maximum when an NC sample with a 1:1 mol ratio of alpha-Fe2O3:ZnO was used. This boosted activity is due to the higher charge carriers' separation in the NC sample which elongates the electron/ hole pairs lifetime. For this charge separation process, a matched mole ratio between the NC components requires that achieved when the same moles of ZnO and alpha-Fe2O3 used. The photodegradation rate constant of MB was about 0.0640 min(-1) (t(1/2)= 10.8 min) (in the range of 75-120 min) and 0.0119 min(-1) (t(1/2)= 58.2 min) (in the range of 0-60 min). The mineralization of MB was studied by the chemical oxygen demand (COD) approach and the MB mineralization rate constant of about 0.0192 min(-1) (t(1/2) = 36.1 min) was obtained (in the range of 0-60 min).